This invention relates to a flat sealing gasket, particularly a cylinder head gasket used in an internal combustion engine. The gasket has several large circular openings for alignment with a respective combustion chamber of the engine. The gasket edge defining each such opening is framed by a sheet metal armor and further, along such gasket edge means are provided to improve the sealing conditions.
Cylinder head gaskets for internal combustion engines comprise soft-material mats which may be metal-reinforced or steel sheet plates. Particularly for protecting the gasket edges surrounding the combustion chambers from the effects of the hot combustion gases and for the purpose of increasing the sealing pressure, the edges defining the openings are framed by means of an armor made of sheet metal and having an approximately U-shaped cross section. The legs of the U extend on opposite sides of the gasket mat in a face-to-face engagement therewith. For improving the sealing effect it is known to insert sheet metal rings of, for example, circular or rectangular cross section or elastic coil spring rings along the gasket edge in the zone surrounded by the armor. Further, forepieces constituted usually by metal rings at the gasket edges are also known.
U.S. Pat. No. 4,397,472 discloses a metal-reinforced soft-material cylinder head gasket whose metal plate projects radially inwardly along the gasket edge (which defines an opening to be aligned with a combustion chamber) and is deformed there to constitute an annular bead. The hollow space enclosed by the bead is filled with graphite and is surrounded by a metallic frame or armor.
High elasticity and only a slight thermosetting property are significant conditions for an optimal sealing behavior at the combustion chamber edge of the cylinder head gasket. By virtue of the stresses during engine operation, however, at the gasket edge a continuous oscillating stress is present due to the significant axial oscillations of the associated engine cylinder. The coil spring rings inserted into the metal frames and also the inserted or adjacently positioned metal rings lose at least some of their resilient properties due to the additionally present significant heat stress and further, there may occur a significant thermosetting at the gasket edge in a non-uniform distribution about the circumference, eventually resulting in leakages at the seal.